U.S. patent number 7,546,689 [Application Number 11/775,081] was granted by the patent office on 2009-06-16 for joint for coordinate measurement device.
This patent grant is currently assigned to Hexagon Metrology AB. Invention is credited to Paul Ferrari, Dongmei Hong.
United States Patent |
7,546,689 |
Ferrari , et al. |
June 16, 2009 |
Joint for coordinate measurement device
Abstract
An articulating joint for a coordinate measurement machine can
include an improved optical encoder. The optical encoder can have
an encoder hub and a read head that are rotatable with respect to
each other based on movement of the articulating joint about an
axis of rotation of the joint. The encoder hub has a read surface.
The read surface can be an outer surface of a generally cylindrical
segment. The read head can be positioned such that a read direction
defined by the read surface is generally perpendicular to the axis
of rotation of the articulating joint.
Inventors: |
Ferrari; Paul (Carlsbad,
CA), Hong; Dongmei (San Diego, CA) |
Assignee: |
Hexagon Metrology AB (Nacka
Strand, SE)
|
Family
ID: |
40251931 |
Appl.
No.: |
11/775,081 |
Filed: |
July 9, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090013547 A1 |
Jan 15, 2009 |
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Current U.S.
Class: |
33/503; 33/1N;
33/1PT |
Current CPC
Class: |
G01B
5/0014 (20130101) |
Current International
Class: |
G01B
5/008 (20060101); G01B 5/012 (20060101) |
Field of
Search: |
;33/1N,1PT,503,504,706,707,708 ;250/231.13,231.18 |
References Cited
[Referenced By]
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404057690 |
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WO 98/08050 |
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Feb 1998 |
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WO |
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Primary Examiner: Smith; R. Alexander
Attorney, Agent or Firm: Knobbe, Martens, Olson & Bear,
LLP
Claims
What is claimed is:
1. A coordinate measuring machine comprising: a first transfer
member; a second transfer member; and an articulating joint
assembly rotatably coupling the first transfer member to the second
transfer member and defining an axis of rotation, said articulating
joint comprising: a housing; and a shaft rotatable relative to said
housing; and an encoder assembly comprising: a read head coupled to
one of said housing and said shaft; and an encoder hub attached the
other of said housing and said shaft, the encoder hub having a read
surface; wherein said encoder read head and the read surface of the
encoder hub define a read direction of the encoder assembly, and
wherein the read direction is transverse to the axis of rotation of
the articulating joint.
2. The coordinate measuring machine of claim 1, wherein the encoder
hub comprises a tapered mounting surface and the housing of the
articulating joint comprises a tapered mounting surface.
3. The coordinate measuring machine of claim 1, wherein the encoder
hub further comprises optical demarcations positioned on the read
surface.
4. The coordinate measuring machine of claim 3, wherein the optical
demarcations are substantially parallel to the rotational axis of
the articulating joint.
5. The coordinate measuring machine of claim 3, wherein the optical
demarcations comprise grating.
6. The coordinate measuring machine of claim 1, wherein the read
direction of the encoder assembly is substantially perpendicular to
the rotational axis of the articulating joint.
7. The coordinate measuring machine of claim 1, wherein the encoder
hub has a generally cylindrical outer surface defining the read
surface.
8. The coordinate measuring machine of claim 1, wherein the encoder
assembly further comprises a processor operatively coupled to the
read head.
9. The coordinate measuring machine of claim 8, wherein the
processor comprises a printed circuit board.
10. The coordinate measuring machine of claim 9, wherein the
printed circuit board is configured to digitize a signal generated
by the encoder assembly.
11. The coordinate measuring machine of claim 9, wherein the
printed circuit board is retained within one of the first transfer
member and the second transfer member.
12. The coordinate measuring machine of claim 1, further comprising
a second articulating joint assembly rotatably coupling the first
transfer member to the second transfer member and defining a second
axis of rotation such that the first transfer member is rotatably
movable relative to the second transfer member about the second
axis of rotation.
13. The coordinate measuring machine of claim 12, wherein the
second articulating joint comprises: a housing; and a shaft
rotatable relative to said housing; and an encoder assembly
comprising: a read head rotationally coupled to one of said housing
and said shaft; and an encoder hub attached to the other of said
housing and said shaft, the encoder hub having a read surface;
wherein said read head and the read surface of the encoder hub
define a read direction of the encoder assembly, and wherein the
read direction is transverse to the axis of rotation of the
articulating joint.
14. The coordinate measuring machine of claim 13, wherein the
encoder hub has a generally cylindrical outer surface defining the
read surface.
15. The coordinate measuring machine of claim 13, wherein the read
head is rotationally coupled to said housing and the encoder hub is
attached to the shaft.
16. A coordinate measuring machine comprising: a manually
positionable articulated arm having opposed first and second ends,
said arm including a plurality of arm segments connected together
by joints, each joint rotating about a rotational axis, a
measurement probe attached to a first end of said articulated arm;
and a plurality of encoders, wherein at least one of said encoders
comprises an encoder hub that rotates about the rotational axis of
the joint and an encoder read head, the encoder hub including
gratings that extend in a direction that is substantially parallel
to the rotational axis of the articulating joint.
17. The coordinate measuring machine of claim 16, wherein the read
direction of the encoder read head is substantially perpendicular
to the rotational axis of the joint.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present application relates to measuring devices, and more
particularly, to articulated arm coordinate measurement machines
for measuring the coordinates of three-dimensional objects.
2. Description of the Related Art
Rectilinear measuring systems, also referred to as coordinate
measuring machines (PCMM's) and articulated arm measuring machines,
are used to generate geometry information. In general, these
instruments capture the structural characteristics of an object for
use in quality control, electronic rendering and/or duplication.
One example of a conventional apparatus used for coordinate data
acquisition is a portable coordinate measuring machine (PCMM),
which is a portable device capable of taking highly accurate
measurements within a measurement sphere of the device. Such
devices often include a probe mounted on an end of an arm that
includes a plurality of transfer members connected together by
joints. The end of the arm opposite the probe is typically coupled
to a moveable base. Typically, the joints are broken down into
singular rotational degrees of freedom, each of which is measured
using a dedicated rotational transducer. During a measurement, the
probe of the arm is moved manually by a user to various points in
the measurement sphere. At each point, the position of each of the
joints must be determined at a given instant in time. Accordingly,
each transducer outputs an electrical signal that varies according
to the movement of the joint in that degree of freedom. Typically,
the probe also generates a signal. These position signals and the
probe signal are transferred through the arm to a
recorder/analyzer. The position signals are then used to determine
the position of the probe within the measurement sphere. See e.g.,
U.S. Pat. Nos. 5,829,148 and 7,174,651.
As mentioned above, the purpose of PCMM's is to take highly
accurate measurements. Accordingly, there is a continuing need to
improve the accuracy of such devices.
SUMMARY OF THE INVENTION
In one embodiment, a coordinate measuring machine is disclosed. The
coordinate measurement machine comprises a first transfer member, a
second transfer member, and an articulating joint assembly. The
articulating joint assembly rotatably couples the first transfer
member to the second transfer member and defines an axis of
rotation. The articulating joint comprises a housing, a shaft, and
an encoder assembly. The shaft is rotatable relative to said
housing. The encoder assembly comprises a read head coupled to one
of said housing and said shaft; and an encoder hub attached to the
other of said housing and said shaft, the encoder hub having a read
surface. The encoder read head and the read surface of the encoder
hub define a read direction of the encoder assembly. The read
direction is transverse to the axis of rotation of the articulating
joint.
In another embodiment, an optical encoder is disclosed. The optical
encoder comprises a housing, a shaft, an encoder hub, and a read
head. The shaft is rotationally coupled to the housing and defines
an axis of rotation. The encoder hub is disposed on the shaft. The
encoder hub defines a read surface. The read head is rotationally
fixed with respect to the housing. A read direction defined by the
position of the read head with respect to the read surface is
transverse to the axis of rotation of the shaft.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features, aspects, and advantages of the present
invention will now be described in connection with preferred
embodiments of the invention, in reference to the accompanying
drawings. The illustrated embodiments, however, are merely examples
and are not intended to limit the invention. The drawings include
the following Figures.
FIG. 1 is a perspective view of one embodiment of a coordinate
measuring machine.
FIG. 2 is cross-sectional view of an articulating member assembly
of the coordinate measuring machine of FIG. 1.
FIG. 3 is an enlarged cross-sectional view of the articulating
member assembly of the coordinate measuring machine of FIG. 1.
FIG. 4 is a perspective view of the articulating member assembly of
the coordinate measuring machine of FIG. 1 with a cover
removed.
FIG. 5 is a perspective view of another articulating member of the
coordinate measuring device of FIG. 1.
FIG. 6 is cross-sectional view of the articulating member of FIG.
5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates one embodiment of a coordinate measuring machine
(PCMM) 10. In the illustrated embodiment, the PCMM 10 comprises a
base 20, a plurality of substantially rigid, transfer members 24,
26, and 28, a coordinate acquisition member 30, and a plurality of
articulation members 40, 42, 44, 46, 48, 50 connecting the rigid
transfer members 24, 26, 28 to one another. Each articulation
member is configured to impart one or more rotational and/or
angular degrees of freedom. The articulation members 40, 42, 44,
46, 48, and 50 allow the transfer members 24, 26, 28 of the PCMM 10
to be aligned in various spatial orientations thereby allowing fine
positioning of a coordinate acquisition member 30 in
three-dimensional space.
The position of the rigid transfer members 24, 26, 28 and the
coordinate acquisition member 30 may be adjusted manually, or
using, robotic, semi-robotic, and/or any other adjustment method.
In one embodiment, the PCMM 10, through the various articulation
members 40, 42, 44, 46, 48, 50, is provided with six rotary axes of
movement. However, there is no strict limitation to the number or
order of axes of movement that may be used, and, in other
embodiments, a PCMM can have more or fewer axes of movement.
In the embodiment of PCMM 10 illustrated in FIG. 1, the
articulation members 40, 42, 44, 46, 48, 50 can be divided into two
functional groupings based on their operation, namely: 1) those
articulation members 40, 44, and 48 which allow the swiveling
motion associated with a specific transfer member (hereinafter,
"swiveling joints"), and 2) those articulation members 42, 46, and
50 which allow a change in the relative angle formed between two
adjacent members or between the coordinate acquisition member 30
and its adjacent member (hereinafter, "hinge joints"). While the
illustrated embodiment includes three swiveling joints and three
hinge joints positioned as to create six axes of movement it is
contemplated that in other embodiments, the number of and location
of hinge joints and swiveling joints can be varied to achieve
different movement characteristics in a PCMM. For example, a
substantially similar device with seven axes of movement could
simply have an additional swivel joint between the coordinate
acquisition member 30 and articulation member 50.
The coordinate acquisition member 30 can comprise a contact
sensitive member or hard probe 32 configured to engage surfaces of
a selected object and/or generate coordinate data on the basis of
probe contact as is known in the art. Alternatively, the coordinate
acquisition member 30 can comprise a remote scanning and detection
component that does not necessarily require direct contact with the
selected object to acquire geometry data. In one embodiment, a
laser coordinate detection device (e.g., laser camera) can be used
to obtain geometry data without direct object contact. It will be
appreciated that in various embodiments of PCMMs, various
coordinate acquisition member 30 configurations can be used
including: a contact-sensitive probe, a remote-scanning probe, a
laser-scanning probe, a probe that uses a strain gauge for contact
detection, a probe that uses a pressure sensor for contact
detection, a probe that used an infrared beam for positioning, and
a probe configured to be electrostatically-responsive. Each of
these can be used for the purposes of coordinate acquisition.
With continued reference to FIG. 1, in various embodiments of the
PCMM 10, the various devices which may be used for coordinate
acquisition, such as the probe 32, may be configured to be manually
disconnected and reconnected from the PCMM 10 such that a user can
change coordinate acquisition devices without specialized tools.
Thus, a user can quickly and easily remove one coordinate
acquisition device and replace it with another coordinate
acquisition device. Such a connection may comprise any quick
disconnect or manual disconnect device. This rapid connection
capability of a coordinate acquisition device can be particularly
advantageous in a PCMM 10 that can be used for a wide variety of
measuring techniques (e.g. measurements requiring physical contact
of the coordinate acquisition member with a surface followed by
measurements requiring only optical contact of the coordinate
acquisition member) in a relatively short period of time.
In the embodiment of FIG. 1, the coordinate acquisition member 30
also comprises buttons 66, which are configured to be accessible by
a user. By pressing one or more of the buttons 66 singly, multiply,
or in a preset sequence, the user can input various commands to the
PCMM 10. In some embodiments the buttons 66 can be used to indicate
that a coordinate reading is ready to be recorded. In other
embodiments the buttons 66 can be used to indicate that the
location being measured is a home position and that other positions
should be measured relative to the home position. In other
embodiments the buttons may be used to turn on or off the PCMM 10.
In other embodiments, the buttons 66 can be programmable to meet a
user's specific needs. The location of the buttons 66 on the
coordinate acquisition member 30 can be advantageous in that a user
need not access the base 20 or a computer in order to activate
various functions of the PCMM 10 while using the coordinate
acquisition member 30. This positioning may be particularly
advantageous in embodiments of PCMM having transfer members 24, 26,
or 28 that are particularly long, thus placing the base 20 out of
reach for a user of the coordinate acquisition member 30. In some
embodiments of the PCMM 10, any number of user input buttons (e.g.,
more or fewer than the three illustrated in FIG. 1), can be
provided, which may be placed in various other positions on the
coordinate acquisition member 30 or anywhere on the PCMM 10. Other
embodiments of PCMM can include other user input devices positioned
on the PCMM or the coordinate acquisition member 30, such as
switches, rotary dials, or touch pads in place of, or in addition
to user input buttons.
With continued reference to FIG. 1, in some embodiments, the base
20 further comprises magnetic attachment mounts 60 that can attach
the base 20 to a metallic work surface. The magnetic attachment
mounts 60 can desirably be selectively engaged so that a user can
position the PCMM 10 on to a work surface then engage the magnetic
attachment mounts 60 once the PCMM 10 has been placed in a
desirable position. In other embodiment, the base 20 can be coupled
to a work surface through a vacuum mount, bolts or other coupling
devices. Additionally, in some embodiments, the base 20 can
comprise various electrical interfaces such as plugs, sockets, or
attachment ports 62. In some embodiments, attachment ports 62 can
comprise connectability between the PCMM 10 and a USB interface for
connection to a processor such as a general purpose computer, an AC
power interface for connection with a power supply, or a video
interface for connection to a monitor. In some embodiments, the
PCMM 10 can be configured to have a wireless connection with an
external processor or general purpose computer such as by a WiFi
connection, Bluetooth connection, RF connection, infrared
connection, or other wireless communications protocol. In some
embodiments, the various electrical interfaces or attachment ports
62 can be specifically configured to meet the requirements of a
specific PCMM 10.
With continued reference to FIG. 1, in some embodiments, the base
20 of the PCMM 10 can also include a self contained power source 64
such as a battery. Embodiments of PCMM 10 having a self contained
power source can be easily moved to various locations that do not
have easy access to a power source such as an AC power outlet,
allowing enhanced flexibility in the operating environment of the
PCMM 10. In one embodiment, the self-contained power source 64 can
be a lithium-ion rechargeable battery that can provide power to the
PCMM for periods of use away from a power outlet. In other
embodiments, the self-contained power source 64 can be other types
of rechargeable batteries such as nickel cadmium, nickel metal
hydride, or lead acid batteries. In other embodiments, the
self-contained power source 64 can be a single use battery such as
an alkaline battery.
With continued reference to FIG. 1, the transfer members 24, 26,
and 28 are preferably constructed of hollow generally cylindrical
tubular members so as to provide substantial rigidity to the
members 24, 26, and 28. The transfer members 24, 26, and 28 can be
made of any suitable material which will provide a substantially
rigid extension for the PCMM 10. As will be discussed in greater
detail below, the transfer members 24, 26, and 28 preferably define
a double tube assembly so as to provide additional rigidity to the
transfer members 24, 26, and 28. Furthermore, it is contemplated
that the transfer members 24, 26, and 28 in various other
embodiments can be made of alternate shapes such as those
comprising a triangular or octagonal cross-section.
In some embodiments, it can be desirable to use a composite
material, such as a carbon fiber material, to construct at least a
portion of the transfer members 24, 26, and 28. In some
embodiments, other components of the PCMM 10 can also comprise
composite materials such as carbon fiber materials. Constructing
the transfer members 24, 26, 28 of composite such as carbon fiber
can be particularly advantageous in that the carbon fiber can react
less to thermal influences as compared to metallic materials such
as steel or aluminum. Thus, coordinate measurement can be
accurately and consistently performed at various temperatures. In
other embodiments, the transfer members 24, 26, 28 can comprise
metallic materials, or can comprise combinations of materials such
as metallic materials, ceramics, thermoplastics, or composite
materials. Also, as will be appreciated by one skilled in the art,
many of the other components of the PCMM 10 can also be made of
composites such as carbon fiber. Presently, as the manufacturing
capabilities for composites are generally not as precise when
compared to manufacturing capabilities for metals, generally the
components of the PCMM 10 that require a greater degree of
dimensional precision are generally made of a metals such as
aluminum. It is foreseeable that as the manufacturing capabilities
of composites improved that a greater number of components of the
PCMM 10 can be also made of composites.
With continued reference to FIG. 1, some embodiments of the PCMM 10
may also comprise a counterbalance system 80 that can assist a user
by mitigating the effects of the weight of the transfer members 26
and 28 and the articulating members 44, 46, 48, and 50. In some
orientations, when the transfer members 26 and 28 are extended away
from the base 20, the weight of the transfer members 26 and 28 can
create difficulties for a user. Thus, a counterbalance system 80
can be particularly advantageous to reduce the amount of effort
that a user needs to position the PCMM for convenient measuring. In
some embodiments, the counterbalance system 80 can comprise
resistance units (not shown) which are configured to ease the
motion of the transfer members 26 and 28 without the need for heavy
weights to cantilever the transfer members 26 and 28. It will be
appreciated by one skilled in the art that in other embodiments
simple cantilevered counterweights can be used in place or in
combination with resistance units.
In the embodiment illustrated in FIG. 1, the resistance units are
attached to the transfer member 26 to provide assisting resistance
for motion of the transfer members 26 and 28. In some embodiments,
the resistance units can comprise hydraulic resistance units which
use fluid resistance to provide assistance for motion of the
transfer members 26 and 28. In other embodiments the resistance
units may comprise other resistance devices such as pneumatic
resistance devices, or linear or rotary spring systems.
With continued reference to FIG. 1, the position of the probe 32 in
space at a given instant can be calculated if the length of each
transfer member 24, 26, and 28 and the specific position of each of
the articulation members 40, 42, 44, 46, 48, and 50 are known. The
position of each of the articulation members 40, 42, 44, 46, 48,
and 50 can be measured as a singular rotational degree of motion
using a dedicated rotational transducer, which will be described in
more detail below. Each transducer can output a signal (e.g., an
electrical signal), which can vary according to the movement of the
40, 42, 44, 46, 48, 50 in its degree of motion. The signal can be
carried through wires or otherwise transmitted to the base 20 of
the PCMM 10. From there, the signal can be processed and/or
transferred to a computer for determining the position of the probe
32 in space.
In some embodiments of PCMM 10, a rotational transducer for each of
the articulation members 40, 42, 44, 46, 48., and 50 can comprise
an optical encoder. Various embodiments of optical encoder are
discussed in more detail below with reference to FIGS. 3-6. In
general, an optical encoder measures the rotational position of an
axle by coupling its movement to a pair of internal hubs having
successive transparent and opaque bands. In such embodiments, light
can be shined through or reflected from the hubs onto optical
sensors which feed a pair of electrical outputs. As the axle sweeps
through an arc, the output of an analog optical encoder can be
substantially two sinusoidal signals which are 90 degrees out of
phase. Coarse positioning can be determined through monitoring a
change in polarity of the two signals. Fine positioning can be
determined by measuring an actual value of the two signals at a
specific time. In certain embodiments, enhanced accuracy can be
obtained by measuring the output precisely before it is corrupted
by electronic noise. Thus, digitizing the position information
before it is sent to the processor or computer can lead to enhanced
measurement accuracy.
As will be described in detail below, in the illustrated
embodiment, the articulation members 40, 42, 44, 46, 48, and 50 can
be divided into two general categories, namely: 1) articulation
members 40, 44, 48, which allow swiveling motion of a transfer
member 24, 26, 28 and are thus sometimes referred to as "swivel
members" 40, 44, 48 herein and 2) articulation members 42, 46 and
50, which allow for change in the relative angle formed between two
adjacent members and are sometimes referred to herein as "pivot or
hinge members" 42, 46, 50.
While several embodiment and related features of a PCMM 10 have
been generally discussed herein, additional details and embodiments
of PCMM 10 can be found in U.S. Pat. Nos. 5,829,148 and 7,174,651,
and the entirety of these patents are hereby incorporated by
reference herein. While certain features below are discussed with
reference to the embodiments of PCMM 10 described above, it is
contemplated that they can be applied in other embodiments of PCMM
such as those described in U.S. Pat. Nos. 5,829,148 or 7,174,651,
or some other pre-existing PCMM designs, or PCMM designs to be
developed.
Referring now to FIG. 2, a cross-sectional view of a transfer
member 26 and articulating member 44 is illustrated. While this
view illustrates a single transfer member 28 in the PCMM 10, other
transfer members 24, 28 of the PCMM 10 can have similar
construction. The transfer member 26 preferably comprises a distal
end 98 and a proximal end 99. As described herein, the terms distal
and proximal are used to describe relative ends of the PCMM 10 and
its associated components with the base 20 being the proximal end
and probe 32 being the distal end (See FIG. 1). The terms distal
and proximal are meant only to simplify description and are in no
way intended to limit the scope of the technology described
herein.
Beginning with the tubular assembly illustrated in FIG. 2, the
transfer member 26 preferably comprises an inner shaft 102 and an
outer housing 104. The inner shaft 102 is preferably configured to
be rotated independently of the outer housing 104 so as to provide
rotational freedom for the transfer member 26. The inner shaft 102
can desirably rotate on a first bearing 118 and also on,
preferably, a compliant bearing 133 that are positioned at opposite
ends of the inner shaft 102 and the outer housing 104. This
configuration is particularly advantageous in that the bearings 118
and 133 are located relatively far apart so as to provide a very
stable rotating interface between the inner shaft 102 and the outer
housing 104. In the illustrated embodiment, the bearings 118, 133
are desirably press fit so as to provide a secure rotating
interface between the inner shaft 102 and the outer housing 104.
Furthermore, in some embodiments, it may be preferable to
appropriately preload the bearings 118, 133 so that any unwanted
axial movement of the inner shaft 102 relative to the outer housing
104 is minimized. In other embodiments, the bearings can be
positioned at different locations to provide a rotating interface
between the inner shaft 102 and the outer housing 104. In still
other embodiments more or fewer than two bearings 118, 133 can
provide a rotating interface between the inner shaft 102 and outer
housing 104 of the transfer member 26. For example, a single
bearing positioned on the proximal end can provide the rotating
interface. In some embodiments, the second bearing 133 is a
compliant bearing including an O-ring 135 extending therearound. In
some embodiments, a bearing 120 of the encoder assembly 128 can be
a compliant bearing, and the two bearings 118, 133 of the transfer
member 26 can be rigid bearings. In some embodiments, bushings can
be substituted for bearings.
As illustrated in FIGS. 1 and 2, both the inner shaft 102 and the
outer housing 104 comprise generally cylindrical members. This
generally cylindrical construction can be advantageous because it
offers construction simplicity, rigidity, light weight, and space
inside for a printed circuit board which will be discussed in
greater detail below. Also, as shown in FIG. 2, the generally
cylindrical shape allows concentric mounting of an inner shaft 102
having an outer diameter approaching the inner diameter of the
outer housing 104, thereby increasing rigidity while maintaining
low weight and a sleek profile. In some embodiments, the outer
diameter of the inner shaft 102 is desirably at least 50%, and more
preferably at least 75% of the inner diameter of the outer housing
104. In some embodiments the inner shaft 102 and outer housing 104
can comprise alternate shapes. For example, in some embodiments,
the inner shaft 102 can comprise a solid shaft as opposed to a
tubular member. Furthermore, in other embodiments the inner shaft
and outer housing 104 can comprise substantially polygonal
cross-sectional profiles such as an octagonal shape, a triangular
shape, or a square shape.
With continued reference to FIG. 2, the inner shaft 102 can
desirably comprise an inner tubular member 106 that comprises a
first end cap 110 and a second end cap 112. Furthermore, the outer
housing 104 can comprise an outer tubular member 108, a first end
cap 114 and a second end cap 116. The assembly of the inner and
outer tubular members 106, 108 can form the transfer member 26. The
transfer member 26 thus formed can provides a substantially rigid
structure defining a reach distance for the PCMM 10.
In some embodiments, the end caps 110, 112, 114, 116 can provide
precision machined bearing surfaces for the bearings 118 and 133.
Further, the end caps 110, 112, 114, 116 can provide precision
concentricity to the articulating member 44. In some embodiments,
it is preferable that the end-caps 110, 112, 114, 116 are bonded to
the tubular members 106 and 108 in such a way that the resulting
inner shaft 102 and outer housing 104 are precisely and accurately
balanced. One method of assuring this balance involves allowing an
adhesive agent such as a glue or epoxy to cure while the bonded
assembly is being rotated. Other suitable securing methods may be
used to secure the end caps 110, 112, 114, and 116 to the tubular
members 106 and 108. In some embodiments of PCMM, such suitable
securing methods can also comprise mechanical fastening means such
as a threaded interface, a plurality of screws or bolts, press fit
(such as interference fit), thermal fit, tapered fit, or any
combinations thereof.
In some embodiments, when the end caps 110, 112, 114, and 116 are
bonded to the tubular members 106 in 108 using an adhesive agent
such as a glue or epoxy, portions of the interior surface of the
inner tubular member 106 and the outer tubular member 108 may be
scored, wire brushed, or otherwise grooved to provide a more
positive bonding surface for the adhesive agent. Likewise,
corresponding surfaces of the end-caps 110, 112, 114, and 116 may
be scored in place of or in addition to tubular member scoring.
In some embodiments, it can be desirable that the end caps 110,
112, 114, 116 comprise a different material than the inner and
outer tubular members 106, 108. Thus, in some embodiments,
precision machined metallic end caps can be used together with
carbon fiber tubular members 106, 108. In these embodiments, the
metallic end caps 110, 112, 114, 116 can provide precision bearing
mounting surfaces while the carbon fiber tubular members 106, 108
can achieve beneficial thermal growth properties. In other
embodiments it may be preferable to construct the entire inner
shaft 102 and the outer housing 104 of a single material, such as
carbon fiber.
In the embodiment illustrated in FIG. 2, the first end cap 110 of
the inner shaft 102, comprises mounting holes 122 positioned
radially around the end cap 110. The mounting holes 122 can be used
to attach another articulating member, such as the articulating
member 46 to the transfer member 26. The mounting holes 122 can
also be used to attach an extending member to the articulating
member 26 so as to provide additional range of movement or reach to
the PCMM 10. For example, in one embodiment, a pair of transfer
members 28 can be coupled to each other to extend the reach of the
device. The illustrated arrangement of the mounting holes 122 is
particularly advantageous in that a relatively large number of
fasteners can be used to secure an additional articulating member
or an additional extension number thus providing a substantially
secure and concentric attachment.
FIG. 3 illustrates a detail view of the articulating member 44 of
FIG. 2. With reference to FIG. 3, a cover piece 124 can be coupled
to the second end cap 116 of the outer housing 104. The cover piece
124 can extend proximally so as to accommodate internal components
of the articulating member 44 which reside towards a proximal end
of the articulating member 44. In the illustrated embodiment, a
slip ring assembly 126 and an encoder assembly 128 are housed
within the cover 124. The slip ring assembly 126, in some
embodiments, can be substantially similar to the slip ring assembly
described in U.S. Pat. No. 5,829,148 issued on Nov. 3, 1998. In
other embodiments, different slip ring assemblies can be housed
with the encoder assembly 128. In still other embodiments, no slip
ring assembly 126 is present. Embodiments of the encoder assembly
128 will be described in detail below.
With continued reference to FIG. 3, in the illustrated embodiment,
the encoder assembly 128 comprises a read head 130, an encoder hub
132, a housing 131, encoder shaft 137 and a bearing 120 mounted
between the housing 131 and encoder shaft 133. In some embodiments,
the bearing 120 can be a compliant bearing. In these embodiments,
both bearings 118, 133 of the transfer member 28 can be rigid. The
encoder hub 132 can be mounted on the encoder shaft 137, which, in
turn, can be inserted into the second end cap 112 of the inner
shaft 102. A hub mounting portion 134 extends proximally from the
encoder hub 132. The hub mounting portion 134 can comprise a
tapered portion over which the encoder hub 132 can mount. In the
illustrated embodiment, the encoder hub 132 preferably comprises a
tapered recess 138 which closely matches a tapered portion 136 of
the hub mounting portion 134. In some embodiments, this matched
tapered fit can rotationally fix the encoder hub 132 to the encoder
shaft 137. In other embodiments, it is desirable that the encoder
hub 132 is further and/or alternatively attached to the hub
mounting portion 134 with fasteners or an adhesive agent in
addition to the tapered fit. The taper mounted design
advantageously allows for the eccentricity between the hub and the
axis to be minimized during mounting of the encoder hub 132 to the
encoder shaft 137. However, in other embodiments, the encoder hub
132 could be mounted directly to the encoder shaft 137 using bolts,
adhesive, press fit or temperature fit with or without a taper
interface. While in the illustrated embodiment, the encoder hub 132
is rotationally fixed to encoder shaft 137, in other embodiments,
the encoder hub 132 can be directly mounted to the inner shaft 102,
the end cap 112 and/or another intermediate member.
In some embodiments, it is preferable that the encoder assembly 128
can be a light emitting diode (LED) encoder design. A reflective
LED encoder design can provide particular advantages in that the
light is reflected back to the read head 130 instead of being
passed through gratings of the encoder hub 132. This reflective
arrangement simplifies the encoder assembly 128 so as to not
require an additional light source to pass light through optical
demarcations or grating of the encoder hub 132. In other
embodiments, a laser light source can be used. In other
embodiments, the encoder can be a magnetic encoder rather than an
optical encoder, and the encoder hub can include a magnetic pattern
disposed thereon. In some embodiments of the encoder assembly 128
the encoder hub 132 is a RESR Taper Mounted Encoder hub as produced
by Renishaw of the UK. Furthermore, in some embodiments the read
head 130 is a type RGH35 also produced by Renishaw of the UK. These
aforementioned devices are strictly examples of a read head and an
encoder hub that can be used with one embodiment of the PCMM 10. In
other embodiments, any suitable read head 130 or encoder hub 132
can also be used.
With continued reference to FIG. 3, in the illustrated embodiment,
the read head 130 and the encoder hub 132 are arranged such that a
read surface 140 of the encoder hub 132 is on a radially outer
surface of the encoder hub 132 and the read head 132 is positioned
radially outwards of the read surface 140. In some embodiments, the
read head 130 can be attached to a bracket 162, which secures the
read head 130 in a relatively stable position relative to the
encoder hub 132. In some embodiments, the bracket 162 may be also
used to secure the slip ring assembly 126 and/or a printed circuit
board which will be discussed in greater detail below. In other
embodiments, the read head 130, slip ring assembly 126, and printed
circuit board can each be retained by separate brackets, or can be
retained by mounting features formed in the surface of the cover
124.
In a preferred embodiment of the encoder, a read direction of the
encoder assembly 128 is substantially perpendicular to the rotation
axis RA of the articulating member, and the optical demarcations or
gratings on the read surface are parallel to the rotation axis RA
of the encoder assembly. This orientation of read direction is in
opposition of a "disc style encoder" in which the read direction is
parallel to a rotation axis RA of the encoder assembly 128 and
gratings are arranged perpendicular relative to the rotation axis
RA of the encoder assembly 128. As noted below, in other
embodiments, other read head and read surface arrangements can be
made. In the illustrated embodiment, optical demarcations or
gratings on the read surface 140 are preferably parallel to a
rotation axis RA of the encoder assembly 128. In some embodiments,
the demarcations can be placed directly on the shaft 137,
eliminating the need for a separate hub or disk. In some
embodiments, the optical demarcations are not substantially
parallel to the rotation axis RA (e.g., the optical demarcations
could be transverse to the RA). In some embodiments, a read
direction of the encoder assembly 128 is transverse to the rotation
axis RA of the articulating member 44. In the illustrated
embodiment, the read direction of the encoder assembly 128 is
substantially perpendicular to the rotation axis RA of the
articulating member. It is contemplated that still other
embodiments of encoder assembly can include various combinations of
read direction configuration and optical demarcation orientation.
For example, it is contemplated that some embodiments, an encoder
can have a read direction that is transverse to the rotation axis
RA and optical demarcations that are not substantially parallel to
the rotation axis RA (e.g., the optical demarcations could be
transverse to the RA).
The preferred configuration of read direction described above can
be particularly advantageous in that the circumference that the
demarcations are placed on is greater than it would be for a disc
style encoder of the same diameter. This increased circumference
can yield a larger number of demarcations per revolution, thus
increasing the resolution of the axis. This fine resolution is
achieved in part because the read surface 148 is placed on a
radially outer surface of the encoder hub 132, thus providing a
relatively large readable surface area on the encoder hub 132.
Thus, in some embodiments of optical encoder assembly 128 having
optical demarcations on the read surface 140 of the encoder hub
132, there are a greater number of optical demarcations. This fine
resolution is particularly advantageous in a PCMM 10 because the
greater the resolution that can be achieved by the encoder assembly
128, the greater the accuracy of the measurement that can be
achieved by the PCMM 10.
In a "disc style encoder", the read head and the encoder disc are
arranged in a direction such that they can be detrimentally
affected by thermal expansion. In these disc-style encoders, the
inner shaft 102 and the bracket 162 could change in dimensions by
differing amounts under certain conditions in response to
temperature variations, causing the read head to move closer to or
further away from the grating. This thermal response by the
disc-style encoder could greatly affect the accuracy of readings by
the encoder under certain thermal conditions. However, in the
embodiments of encoder assembly 128 described above, the read
surface 140 and read head 130 are positioned such that the read
direction is perpendicular to the rotation axis RA. Thus, the
change in encoder signal due to temperature variations is greatly
reduced. This improved thermal response can in part be attributed
to the fact that if thermal expansion does take place it is less
likely to affect the distance between the read head 130 in the
encoder hub 132 because the read head 130 and the encoder hub 132
are located on surfaces which are generally thermally similar.
Furthermore, if thermal expansion were to take place, it is likely
that the encoder hub 132 would simply displace laterally relative
to the read head 130, thus minimally affecting the accuracy of the
encoder assembly 128 as compared to thermal expansion which may
influence the distance between the read head 130 and the encoder
hub 132.
While a particular configuration of read head 130 and encoder hub
132 is illustrated, other embodiments are contemplated. In one
embodiment, the encoder hub 132 can be externally mounted with
respect to the housing 124. This external mounting arrangement
allows for easy setup and alignment of the encoder hub 132 to the
hub mounting portion 134. In another embodiment both the encoder
hub 132 and read head 130 can be located outside of the cover 124
for easy alignment of the read head 130 to the encoder hub 132. In
yet another embodiment, the encoder hub 132 may be surrounded by a
portion of the cover 124, but the read head 130 is external to the
cover 124. In yet another embodiment both the read head 130 and the
encoder hub 132 are internal to the cover 124.
In various other embodiments, it can be desirable to use an encoder
assembly 128 which comprises multiple read heads 130. For example,
in some embodiments, the encoder assembly 128 may comprise three
read heads 130 positioned at approximately 120.degree. intervals
around the encoder hub 132 such that the read heads 130 read the
read surface 140 at multiple locations. This arrangement of read
heads 130 may be particularly advantageous if any eccentricity is
present in the encoder hub 132 as the multiple read heads 130 can
cross check one another and reduce any inaccuracy produced by
eccentricity of the encoder hub 132. Furthermore, it is also
contemplated that in one embodiment of the encoder assembly 128,
multiple read heads 130 can be included while data may be collected
from only one read head 130 at any given time. In various
embodiments, any number of read heads 130 can be used with the most
common being 1, 2, 3, or 4.
With continued reference to FIG. 3, the second end cap 116 of the
outer housing 104 preferably is also attached to a mounting clamp
142 that provides a mounting location for the articulating member
44 to mount to another articulating member assembly. The mounting
clamp 142 can comprise a mounting base 148, which, in some
embodiments, can be integrally formed with the end cap 116. The
mounting base 148 preferably extends from the articulating member
44 and is attached to a face plate 146 by fasteners 144. The face
plate 146 and the mounting base 148 can define a mounting hole 150
which is configured to attach to an axle of another articulating
member assembly as described in greater detail below.
With reference to FIG. 4, a proximal end of the articulating member
44 is illustrated with the cover 124 removed for clarity. In some
embodiments, the articulating member 44 preferably also comprises a
processor such as a printed circuit board 160 operatively coupled
to the encoder assembly 128. The printed circuit board 160
preferably can be used to process an electronic signal generated by
the encoder assembly 128. In some embodiments, the printed circuit
board 160 can be used to convert an analog signal generated by the
encoder assembly 128 to a digital signal. The printed circuit board
160 can be operatively coupled to a processor or other computer via
a wired or wireless link and can transmit the digital signal to the
processor or computer. In the illustrated embodiment, the printed
circuit board is desirably located proximally of the encoder hub
132 and is further supported by the bracket 162. In some
embodiments, the bracket 162 can be also configured to support the
slip ring assembly 126 and/or the read head 130 (see FIG. 3). The
location of the printed circuit board 160, as illustrated in FIG. 4
can be particularly advantageous in that it provides a relatively
out-of-the-way position for the printed circuit board such that the
operation of the encoder assembly 128 and the slip ring assembly
126 are not impeded by the printed circuit board 160. Furthermore,
in the illustrated embodiments, the printed circuit board 160 is
housed within the cover 124, thus providing protection from bumping
or contamination. In other embodiments, other positions for the
printed circuit board 160 may also be employed, such as that
illustrated in FIG. 5 described in greater detail below.
FIG. 5, illustrates the articulation member or hinge member 46 of
FIG. 1 decoupled from the transfer member 26 and the transfer
member 28. The articulation member 46 can comprise a housing yoke
202 supporting a shaft 204. In some embodiments of PCMM 10, the
shaft 204 can be clamped by a mounting clamp associated with the
articulating member 48, similar to the mounting clamp 142 of the
articulating member 44 (FIG. 3). The housing yoke 202 can desirably
support the shaft 204 at two locations so as to provide an exposed
region of the shaft 202. This exposed region of the shaft 204 can
be clamped by the mounting clamp 142. In the illustrated
embodiments, the housing yoke 202 extends downwards to a mounting
member 206 comprising mounting holes 208 As illustrated, the
mounting holes 208 configured to mate with the holes 122 of the
transfer member 26(see FIG. 2). In some embodiments, a cover 210 is
attached to one external side of the housing yoke 202. The cover
210 is configured to house internal workings of the articulating
member 46. In some embodiments, an encoder assembly is housed
within the cover 210.
FIG. 6 is an illustration of a cross-sectional view of the
articulating member 46 of FIG. 5. In some embodiments, the
articulating member 46 comprises bearings 216, 218 which support
opposing ends of the shaft 204 so as to provide a smooth rotational
interface for the shaft 204 relative to the housing yoke 202. In
some embodiments, the shaft 204 can include an encoder mount
portion 220. In some embodiments, the mount portion 220 can be
formed to a tapered mount portion 222 configured to receive an
encoder hub 224. The encoder hub 224 can comprises a tapered recess
226 which is sized and shaped to closely receive the tapered mount
portion 222 of the shaft 204.
Similar to the encoder assembly illustrated in FIG. 3 above with
respect to a swiveling articulation member, the encoder assembly
212 illustrated in FIG. 6 comprises an encoder hub 224 and a read
head 230. The encoder hub 224 can comprise a read surface 228 that
is located on a radially outer surface thereof. Furthermore, the
read head 230 can be mounted to the housing yoke 202. The read head
can be configured to read optical demarcations on the read surface
228 of the encoder hub 224.
Once again, the arrangement of the encoder hub 224 and the read
head 230 can be particularly advantageous in that the read surface
228 is located on the encoder hub 224 such that a relatively large
number of optical demarcations can be placed on the encoder hub
with relatively large spacing between adjacent demarcations. Thus,
relatively fine resolution can be achieved by the encoder assembly
212. Furthermore, in some embodiments, the optical demarcations can
be oriented such that they are substantially parallel to a rotation
axis RA2 of the encoder assembly 212. Furthermore, similar to the
encoder assembly 128 described above with respect to FIG. 3, the
relative positioning of the encoder hub 224 and the read head 230
can orient the read direction of the optical encoder assembly 212
transversely to the rotational axis RA2 of the encoder assembly
212. In some embodiments, the read direction of the encoder
assembly 212 can be substantially perpendicular to the rotation
axis RA2.
With continued reference to FIG. 6, a printed circuit board 214 can
extend below the mounting member 206. The printed circuit board 214
preferably can be used to process an electronic signal generated by
the encoder assembly 212. In some embodiments, the printed circuit
board 214 can be used to convert an analog signal generated by the
encoder assembly 128 to a digital signal. The printed circuit board
214, like the printed circuit board 160, can be operatively coupled
to a processor or other computer via a wired or wireless link and
can transmit the digital signal to the processor or computer. One
particular advantage of the location of the printed circuit board
214 is that when the articulating member 46 is assembled with the
transfer member 26 (FIG. 1), the printed circuit board 214 will
preferably extend within the transfer member 26. Thus, the transfer
member 26 can provide a protective covering for the printed circuit
board 214. This covering arrangement can be particularly
advantageous in that the transfer member 26 achieves a dual purpose
by acting as both a protective member and a structural member of
the PCMM 10.
Although this invention has been disclosed in the context of
certain preferred embodiments and examples, it will be understood
by those skilled in the art that the present invention extends
beyond the specifically disclosed embodiments to other alternative
embodiments and/or uses of the invention and obvious modifications
and equivalents thereof. In addition, while the number of
variations of the invention have been shown and described in
detail, other modifications, which are within the scope of this
invention, will be readily apparent to those of skill in the art
based upon this disclosure. It is also contemplated that various
combinations or subcombinations of the specific features and
aspects of the embodiments may be made and still fall within the
scope of the invention. Accordingly, it should be understood that
various features and aspects of the disclosed embodiments can be
combined with, or substituted for, one another in order to perform
varying modes of the disclosed invention. Thus, it is intended that
the scope of the present invention herein disclosed should not be
limited by the particular disclosed embodiments described above,
but should be determined only by a fair reading of the claims.
* * * * *